1. Field of the Invention
The present invention relates to an air reefing system of the type to be used primarily in combination with a flexible flow form device, and specifically to air reefing means disposed on the device.
2. Description of the Prior Art
For as long as man has been utilizing parachute structures, he has recognized serious problems associated with opening the parachute upon its deployment and coping with the tremendous opening shock normally associated with the inflation of parachute devices. In recognition of these problems, numerous devices are known in the prior art for insuring that parachutes will open, and for reducing the attendant opening shock. These prior art devices are generally referred to as reefing assemblies and generally take the form of various restraining means, whereby inflation of the parachute may be controlled in a predetermined fashion. Such devices are generally thought of as contributing positively to both the comfort and safety of parachute deployment. However, a study of the prior art devices reveals that numerous problems associated with reefing assemblies remain unsolved. Most importantly, prior art reefing assemblies simply are not sufficiently reliable in operation.
U.S. Pat. No. 3,278,143, discloses a parachute canopy reefing at panel center lines. The mid-panel reefing means is mounted inside the base of the canopy on a reinforcing band around the bottom edge portion of the canopy and basically comprises reefing line guide rings, a reefing line, and reefing line cutters. By its terms, the mid-panel reefing means is limited in its application to those parachute canopys in which the shroud lines are connected around the canopy to the skirt at equal circumferentially spaced points. It is therefore apparent that the reefing means disclosed by this patent would not be applicable to today's ram air parachutes. Just as clearly, this reefing means would have no application to the flow form device disclosed in my presently pending application referred to above. However, dismissing its inapplicability to various specific parachute structures, the reefing means disclosed therein is clearly subject to mechanical malfunction because of its construction. The reefing means cannot operate properly if the reefing line becomes twisted or tangled. Failure of the reefing line cutters to operate properly would prevent the parachute from fully inflating. Finally, as the reefing line is pulled through the reefing line guide rings, the resultant frictional forces create heat which could result in burning through the parachute canopy.
A rereefing parachute assembly and system is disclosed in U.S. Pat. NO. 3,434,680. An express purpose of the invention disclosed therein is to provide an improved parachute suitable for towing which may be released while in tow and will then reopen to allow the payload to make a normal descent. This reopening, or rereefing, effect is accomplished by means of the suspension and rigging assembly disclosed therein. The suspension and rigging system result in a pulling down of the central portion of the main parachute, which provides a much larger area over which the opening shock pressures are distributed. This distribution of pressure during opening minimizes damage to the canopy of the main parachute. However, because the assembly depends on its suspension and rigging for its effectiveness, the device is still subject to mechanical malfunction resulting primarily from tangled lines. Furthermore, such a construction has been known to result in complete failure as a result of canopy inversion.
U.S. Pat. No. 3,506,225, relating to an opening shock inhibitor for parachutes, discloses the use of one or more reefer straps secured at fixed locations to the canopy and/or the load lines and wrapped thereabout so as to slowly unwind after the canopy is released from its enclosure and the load lines are deployed. This patent teaches that unwrapping of the reefers delays inflation of the canopy to regulate opening shock. The disclosure of this patent further teaches that the effectiveness of the reefer strap in delaying complete inflation in opening of the parachute is enhanced by preventing unwrapping of the strap until inflation of the canopy has begun. This result is accomplished through the use of releasable holding devices comprising "Velcro" fabric fastener portions mounted on the reefer strap. In effect then, a parachute employing these shock inhibitors is tied together at predetermined points by the reefer strap. Internal pressures resulting from inflation of the parachute canopy overcome the restraining forces of the reefer straps, thus breaking their hold and allowing the parachute to fully inflate. Obviously, if sufficient internal pressure is not created to overcome the restraining force of the reefer straps, the parachute cannot perform its intended preface. Just as obviously, if the reefer straps release prematurely, there will be no inhibition of opening shock.
A pilot chute controlled inflation system for parachutes is disclosed in U.S. Pat. No. 3,540,684. The drag of a pilot chute initiates inflation of a canopy to which it is connected by at least one continuous reefing line having a timed length to regulate dereefing and opening of the canopy. The drag force of the pilot chute is distributed in a stabilizing surface to the canopy at spaced locations by guide rings through which the reefing line extends. In fact, the embodiment of this invention shown in FIG. 4 is used today on substantially all ram air parachutes. With particular reference to this embodiment, it should be noted that ram air parachutes depend upon maintaining approximately a 28.degree. angle of attack along their leading edge to fly properly. Their construction accordingly results in the creation of areas of relatively greater air pressure at the two outboard edges of the device, and an area of relatively least air pressure at the center of the device. Thus, ram air parachutes tend to inflate from their outboard edges toward the middle. Such inflation necessarily creates flight instability during the opening sequence, and may even result in complete failure of the device. Accordingly, the system disclosed in U.S. Pat. No. 3,540,684, has as one of its primary objectives, means for reversing the normal opening sequence of ram air parachutes. That is, the device of this patent "forces" the ram air parachute to open from the middle, outwardly. This result is accomplished by the drag force of the pilot chute on the reefer lines tending to collapse the outboard cells toward the middle of the ram air parachute. Of course, inflation of the parachute pulls against, and subsequently overcomes, this pilot chute drag force.
It is therefore apparent that the effectiveness of the pilot chute controlled inflation system relates most directly to the size of the pilot chute. As the main parachute opens, the pilot chute is in its wake; therefore, its drag is reduced. Reefing then becomes a matter of friction between the reefing lines and the corresponding guide rings. Unfortunately, the friction of the reefing line as it passes through the guide rings and as it passes over the top surface of the parachute often results in burns and tears, resulting in parachute failure. Similarly, if the reefing line becomes twisted or tangled about itself or about the guide rings, the parachute cannot inflate properly. Finally, since the operation of this system is most directly related to the size of the pilot chute, if the pilot chute does not inflate properly, the main parachute will not properly inflate.
Yet another attempt at solving the problems associated with parachute opening shock is shown in U.S. Pat. No. 3,642,237, relating to a spiral reefed variable drag parachute. That patent teaches the use of a plurality of reefing lines positioned about the parachute canopy in a spiral shaped manner whereby the drag of the parachute is varied by actuating control means. This device is particularly susceptible to malfunction occasioned by tangling and twisting of the many reefing lines. The device is furthermore susceptible to malfunction as a result of burning and tearing the parachute canopy as the reefing lines pass through their respective grommets.
Finally, U.S. Pat. No. 3,652,041, discloses a reefing device including a cord or band disposed in confining relation around the parachute and connected to a releasing means which is responsive to the amount and duration of the forces applied thereto. Until it is released, the band encircles the canopy and serves to restrain the canopy so as to retard its full deployment until it has been disconnected by the releasing means. Accordingly, the releasing means is the critical element of this reefing device. The releasing means is disclosed as comprising a cylinder and piston assembly including a cylinder and a piston which are relatively movable in response to forces applied to the band placed in restraining relation around the canopy. Obviously, if the cylinder and piston assembly fails, the parachute will not open properly. Even if this reefing device does function properly, it is undesirable because of its mechanical complexity. This mechanical complexity not only increases its probable failure rate and maintenance requirements, but also results in a relatively expensive reefing device.
It is thus apparent that there is a great need in the art for a reefing system which eliminates the problem of opening shock to the maximum possible extent without interferring with the parachute's normal opening sequence. For reasons of safety and economy, the reefing assembly should be self-operating, requiring no external control means. For these same reasons the reefing system should comprise the fewest possible number of elements in addition to the basic parachute structure. Ideally, the basic reefing system would in fact comprise the parachute structure, with reefing means added for the purpose of enhancing the parachute's self-reefing tendencies. Of course, the dangers normally associated with friction and tangling in present reefing systems must be eliminated to the maximum possible extent. Additionally, such a reefing system should utilize existing air flow pressures created within and without the device in a manner that will not detract from the device's stability and maneuverability characteristics. Finally, such a reefing system should automatically disengage upon substantially full inflation of the device.